<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>导航二级菜单</title>
    <style>
        *{
            margin: 0px;
            padding: 0px;
        }
        ul{
            list-style: none;
        }
        a{
            text-decoration: none;
        }
        .nav{
            width: 960px;
            height: 80px;
            background: orange;
            margin: 0 auto;
        }
        .nav1>li{
            float: left;
            height: 80px;
            line-height: 80px;
            background: lime;
            padding: 0 50px;
        }
        .nav10>li{
            display: none;
            height: 20px;
            line-height: 20px;
        }
        .nav1>li:hover>ul>li{
            display: block;
        }
        .nav1>li:hover>a{
            color: red;
            text-decoration: underline;
        }
        .nav100>li{
            position: relative;
            left:40px;
            top: -20px;
            display: none;
        }
        .nav10>li:hover>.nav100>li{
            display: block;
        }
        .nav1>li>a{
            color: black;
        }
        .nav10>li>a{
            color: black;
        }
        .nav10>li:hover>a{
            color: red;
        }
    </style>
</head>
<body>
<div class="nav">
    <ul class="nav1">
        <li><a href="#">首页</a></li>
        <li>
            <a href="#">产品介绍</a>
            <ul class="nav10">
                <li>
                    <a href="#">语文</a>
                    <ul class="nav100">
                        <li>第一课堂</li>
                        <li>第二课堂</li>
                        <li>第三课堂</li>
                    </ul>
                </li>
                <li><a href="#">数学</a></li>
                <li><a href="#">历史</a></li>
            </ul>
        </li>
        <li>
            <a href="#">在线直播</a>
<!--            <ol class="zhibo">-->
<!--                <li><a href="#">语文1</a></li>-->
<!--                <li><a href="#">数学1</a></li>-->
<!--                <li><a href="#">历史1</a></li>-->
<!--            </ol>-->
        </li>
        <li>
            <a href="#">招聘</a>
<!--            <ol>-->
<!--                <li><a href="#">语文11</a></li>-->
<!--                <li><a href="#">数学12</a></li>-->
<!--                <li><a href="#">历史13</a></li>-->
<!--            </ol>-->
        </li>
        <li>
            <a href="#">关于我们</a>
        </li>
    </ul>
</div>
</body>
</html>